1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to contrast control, and more particularly to controlling contrast according to illumination levels.
2. Description of the Prior Art
Development in digital electronic engineering technologies has led to the digitizing of conventional analog data, and has thus induced emergence of digital-image-signal-processing technologies for digitizing and processing image signals. Usually, digital-image-signal-processing technologies can improve the storage and transmission efficiency of image information by compressing the image information, and can perform various types of image processing: for example, the digital-image-signal-processing technologies can provide an output image that looks better than an input image. As one such digital-image-signal-processing technology, a technology for improving the contrast of an image is being actively researched.
As a representative example of related art technologies for improving the contrast of an image, the luminance histogram equalization technique is widely known. According to the luminance histogram equalization, a luminance histogram of an input image is analyzed, and is then controlled to have a uniform distribution, so as to improve the contrast of the input image. The luminance histogram shows a luminance distribution for pixels within an image, that is, the luminance histogram expresses distribution ranges and values of bright points and dark points within an image.
However, because the related art luminance histogram equalization technique uses only an algorithm depending on a luminance histogram of an input image, it may excessively increase the contrast. As a result, the related art luminance histogram equalization technique may cause an output image to look unnatural.
Also, the related art luminance histogram equalization
technique is problematic in that the brighter the environment, the lower the visibility.